They are not manufactured with a fixed angle for several reasons. The primary reason is that due to inconsistencies in embedding the plastic cassette on the back of the block, the face of the block is just not always going to be flush with the edge of the knife. A secondary reason is to change the angle of the block face to match the knife edge when doing recuts, etc. 
 
Back in the stone age with hinged, L-shaped, and the grid molds the back of the block was never flat so techs became adept at "eyeballing" the angle when the block was put in the microtome clamp. Fine tuning was then done using the adjustment screws. With the introduction of embedding rings and base molds, there was less need for such adjusting and even less need with our present day processing/embedding cassettes and base molds. So I am not surprised that a lot of places have techs who do not ever change their angle. 
 
I agree that it is a necessary skill that should be taught. I also think that adjusting the knife holder back to a neutral position in relation to the knife edge should become part of each microtomes' care, maybe on a weekly basis.
 
Doug Showers MS, HT (ASCP)
Operations Manager
Dermpath Diagnostics
VM 561-712-6283

________________________________

From: histonet-bounces@lists.utsouthwestern.edu on behalf of Rene J Buesa
Sent: Wed 5/14/2008 8:33 AM
To: Hofecker, Jennifer L; Amos Brooks
Cc: histonet
Subject: RE: [Histonet] Standardized Microtomes



They are not manufactured with a "standard angle" because according with the RESISTANCE of the material to cut, due to the intrinsic characteristics of the tissue (more or less "solid" or "resistant") you should experiment with the "ideal angle" for that particular block.
  In the general pathology practice being all human tissues and most of them infiltrated with the same melting point paraffin, they "become" of a "quasi standard" resistance level that can allow a single angle for all microtomes. Under those circumstances it is better to have all microtomes working at the same angle and allowing any HT to recut a block initially cut by any one of the other HTs in the lab.
  René j.

"Hofecker, Jennifer L"  wrote:
  



      
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